Phys Chem Minerals (2007) 34:477–484 DOI 10.1007/s00269-007-0161-y

ORIGINAL PAPER

– Fine structure in photoluminescence spectrum of S2 center in sodalite

Aierken Sidike Æ Alifu Sawuti Æ Xiang-Ming Wang Æ Heng-Jiang Zhu Æ S. Kobayashi Æ I. Kusachi Æ N. Yamashita

Received: 18 December 2006 / Accepted: 6 April 2007 / Published online: 12 June 2007 Springer-Verlag 2007

Abstract The photoluminescence and excitation spectra stretching vibration of the isotopic species of 32S34S–,a 32 – of sodalites from Greenland, Canada and Xinjiang (China) main peak due to that of the isotopic species of S2 and are observed at 300 and 10 K in detail. The features of the five peaks due to phonon sidebands of the main peak. emission and excitation spectra of the orange-yellow flu- – orescence of these sodalites are independent of the locality. Keywords Sodalite Photoluminescence S2 center The emission spectra at 300 and 10 K consist of a broad Heat treatment Fine structure band with a series of peaks and a maximum peak at 648 and 645.9 nm, respectively. The excitation spectra ob- tained by monitoring the orange-yellow fluorescence at 300 Introduction and 10 K consist of a main band with a peak at 392 nm.

The luminescence efficiency of the heat-treated sodalite Natural sodalite represented by the ideal formula Na8Al6 from Xinjiang is about seven times as high as that of un- Si6O24Cl2 or 3(Na2OAl2O32SiO2)2NaCl is a well-known – treated natural sodalite. The emission spectrum of the S2 fluorescent mineral emitting orange-yellow fluorescence center in sodalite at 10 K consists of a band with a clearly under ultraviolet (UV) light. Results of early investigations resolved structure with a series of maxima spaced about were reviewed by Kirk (1954, 1955). Kirk (1954) observed 560 cm–1 (20–25 nm) apart. Each narrow band at 10 K the emission and excitation spectra of the synthetic sodalite shows a fine structure consisting of a small peak due to the 3(Na2OAl2O32SiO2)1.0NaCl0.25Na2S0.25Na2SO4 at 293 and 77 K under 365 nm excitation. The emission spectra extended from about 500 to beyond 700 nm. The emission spectrum at 293 K showed a small amount of structure & A. Sidike A. Sawuti X.-M. Wang H.-J. Zhu ( ) with a most intense peak located at 658 nm, whereas School of Maths–Physics and Information Sciences, Xinjiang Normal University, Urumqi, Xinjiang 830054, China the emission spectrum at 77 K showed a clearly resolved e-mail: [email protected] structure with a series of maxima spaced about 20 nm apart with a most intense peak located beyond 700 nm. S. Kobayashi The excitation spectrum consisted of a structureless band Department of Applied Science, Faculty of Science, Okayama University of Science, Ridai-cho, with a peak at 400 nm (Kirk 1954). Kirk (1955) concluded Okayama 700-0005, Japan that the orange-yellow fluorescence is due to the presence of sodium polysulfide. Later, the orange-yellow fluorescence I. Kusachi – has been assigned to S2 molecule ions in sodalite. The Department of Earth Sciences, Faculty of Education, – – – Okayama University, Tsushima-naka, optical spectra of the O2 ,S2 and Se2 centers in natural Okayama 700-8530, Japan and synthetic sodalites have been reported by some researchers (Hodgson et al. 1967; Taylor et al. 1970; van N. Yamashita Doorn and Schipper 1971; Chang and Onton 1973; Department of Physics, Faculty of Education, Okayama University, Tsushima-naka, Tarashchan 1978; Schlaich et al. 2000; Gaft et al. 2005). Okayama 700-8530, Japan Taylor et al. (1970) observed the emission and excitation 123 478 Phys Chem Minerals (2007) 34:477–484

– – spectra of the S2 center in synthetic chloro-sodalite at substitute for Cl ion that is incorporated into the cage. The 110 K. The emission spectrum with the most intense peak at structure on the orange-yellow emission band of sodalite is about 670 nm consisted of a band structure with a separa- banded due to the symmetric vibration of the diatomic tion of 556 cm–1. The excitation spectrum obtained by sulfur molecules (Tarashchan 1978; Marfunin 1979; monitoring the emission at 600 nm consisted of a struc- Gorobets and Rogojine 2002). tureless band with a peak at about 394 nm (Taylor et al. The objectives of this investigation are (1) to observe 1970). Chang and Onton (1973) synthesized various types the luminescence spectra of natural sodalites from Green- of sodalite. The emission spectra of 3(Na2OAl2O3 land, Canada and Xinjiang (China) in detail, (2) to study 2SiO2)2NaClNa2SO3 under 366 nm excitation consisted the effect of heat treatment on the luminescence efficiency of a band at 300 K with a small amount of structure whose of sodalite and (3) to determine fine structures on emission peak is located at 677 nm and a band at 78 K with a clearly bands at low temperatures. resolved structure whose most intense peak is located at about 680 nm (Chang and Onton 1973). Tarashchan (1978) – observed the emission spectra of the S2 centers in sulfur- Experimental containing aluminosilicate minerals, sodalite, hackmanite, vishnevite, hauyne, lazulite and scapolite. The emission In this investigation, four natural sodalites from Greenland, band of sodalite showed a small amount of structure with Canada and China (Xinjiang; #1 and #2) were analyzed. the most intense peak at about 708 nm. Schlaich et al. Two samples from Xinjiang were obtained from the col- (2000) obtained the absorption spectrum, which was trans- lections of the Xinjiang Geology and Mineral Museum. formed from the diffuse reflectance spectrum, and emission The crystal structures of the samples were examined – spectrum of Se2 in synthetic sodalite at room temperature. using an X-ray powder diffraction system (Rigaku RAD- The absorption spectrum consisted of three absorption bands 1B). The sodalite structure was ascertained by comparing with peaks at 20.00, 28.00 and 40.00 kcm–1. The emission the data with ICDD Card 37-476 for sodalite. spectrum, which was obtained under 28.00 kcm–1-band The chemical compositions of the natural sodalites were excitation at 364 nm (27.47 kcm–1)withanAr+-pumped dye determined by electron probe microanalysis (EPMA) laser, consisted of two bands located in red and blue regions. (JEOL, JXA-8900). Before the measurement by EPMA, the –1 Schlaich et al. (2000) attributedP the 20.00 andP 28.00 kcm surface of each test piece was polished flat and smooth. 2 2 3 – 3 – bands to the g fi u and g fi u transitions, The chemical composition in weight % was determined – respectively, within Se2 P, and red andP blue emission bands to from the mean of the data obtained at ten points of a test 2 2 3 – 3 – the u fi g and u fi g transitions, respec- piece. tively. Gaft et al. (2005)observedthelaser-inducedtime- In preparing sulfur-doped sodalite, grains of natural – resolved luminescence spectra of the S2 center in natural sodalite were sufficiently powdered using an agate mortar. sodalite at 300 and 77 K. A mixture of powder sodalite and sulfur (10–50 wt%) was The optical properties and paramagnetic resonance heated in a quartz crucible at 800–1,100C for 30 min in – – – – spectra of O2 ,S2 , SeS and Se2 ions in various alkali– air. Powder sodalite without sulfur was also heated under halide crystals have been reported by some researchers the same conditions for comparison. After the heat treat- (Rolfe et al. 1961; Rolfe 1964;Kirketal.1965; Rolfe ment, the sample was rapidly quenched to room tempera- 1968; Ikezawa and Rolfe 1973; Rebane and Rebane 1974). ture by placing the crucible on a metal plate at room – The emission spectra of O2 ions in alkali–halides at low temperature and using an air blower. temperatures consist of a series of more than 12 narrow Before the measurement of luminescence spectra, grains bands at intervals of 900-1,100 cm–1 in the blue-green re- of fluorescent sodalite were sufficiently powdered using an gion to the red region (Rolfe et al. 1961; Rolfe 1964; agate mortar. The powdered sample was packed into a – Ikezawa and Rolfe 1973). In the emission spectra of S2 , sample holder with a synthetic quartz-glass cover. – – SeS and Se2 ions in alkali halides, the intervals of the The measuring system of photoluminescence (PL) and narrow bands are about 600–640, 460 and 300 cm–1, excitation spectra was almost the same as that used in respectively (Kirk et al. 1965; Rolfe 1968; Ikezawa and previous studies (Aierken et al. 2006a, b). In the mea- Rolfe 1973). surement of luminescence spectra, a 200 W deuterium – – The luminescence properties of the O2 and S2 centers lamp (Hamamatsu Photonics L1835), a 500 W xenon in minerals are reviewed by Tarashchan (1978), Marfunin short-arc lamp (Ushio UXL-500D) and a 50 W halogen (1979) and Gorobets and Rogojine (2002). The crystal tungsten lamp (Ushio JC12V-50W) were used as excitation structure of the sodalite family is built up from cubo- light sources. octahedral cages of AlO4 and SiO4 groups (Taylor et al. In the measurement of PL spectra, excitation wave- – 1970; Denks et al. 1976). Molecule ion S2 in sodalite can lengths with a bandwidth of 4 nm were selected using a 123 Phys Chem Minerals (2007) 34:477–484 479

Ritsu MC-50L grating monochromator. A band-pass glass Results filter or an interference filter was set in front of the sample to eliminate stray light from the excitation source. Obser- The chemical compositions of the natural sodalites exam- vation wavelengths with a bandwidth of 0.15-1 nm were ined by EPMA are shown in Table 1. The corresponding selected using a Ritsu MC-50 grating monochromator. compositions of sodalite from South Greenland (Markl A suitable glass filter was set in front of the entrance slit et al. 2001) are also shown in Table 1. The determined of the observation monochromator to eliminate reflected compositions (wt%) of Na2O, Al2O3, SiO2 and Cl are radiation from the excitation source. The PL spectral reasonable compared with the theoretical compositions intensity was converted to an electric signal using a pho- calculated from the ideal formula 3(Na2OAl2O32SiO2) tomultiplier (Hamamatsu Photonics R955). The electric 2NaCl of sodalite. The compositions of SO3 in natural signal was input to a personal computer through a GP-IB sodalites from Greenland, Xinjiang (#2), Xinjiang (#1) and cable. The PL spectra were corrected for the spectral sen- Canada are 0.59, 0.11, 0.08 and 0.07 wt%, respectively, in sitivity of the measuring system using a standard tungsten the order of concentration. lamp calibrated according to the National Bureau of Figure 1 shows the PL spectra of the natural sodalites Standards (NBS), USA. from Greenland, Xinjiang (#2), Canada and Xinjiang (#1) In the measurement of optical excitation spectra, the at 300 K under 390 nm excitation. When we rewrite the same measuring system as that used for the emission four spectra normalized at maxima, four curves overlap spectra was used, except that an excitation bandwidth of each other. In other words, the feature of the orange-yellow 1 nm and an observation bandwidth of 5 nm were used. As band of sodalite is independent of the locality of the excitation light sources, three types of lamp corresponding samples. The PL spectrum consists of a broad band with a to the measurement regions were used: a deuterium lamp in small amount of structure and a maximum peak at 648 nm. the 200–320 nm region, a xenon short-arc lamp in the 280– The relative luminescence efficiencies of the orange- 400 nm region and a halogen tungsten lamp in the 360– yellow fluorescence of the four samples from Greenland, 480 nm region. The ordinate of the excitation spectra was Xinjiang (#2), Canada and Xinjiang (#1) are 100, 37, 8 and plotted against the excitation efficiency after optical exci- 6, respectively. tation energy correction. Optical excitation energy was Figure 2a, b shows the emission and excitation spectra measured using a photomultiplier. For a wavelength region of the natural sodalite from Greenland at 300 and 10 K, below 320 nm, optical excitation energy was estimated on respectively. The emission spectrum (Em) in Fig. 2a is the the basis of the excitation spectrum of sodium salicylate, same as curve 1 in Fig. 1. The excitation spectrum obtained which has constant quantum efficiency in this wavelength by monitoring the orange-yellow fluorescence at 300 K region. consists of a main band (Ex) with a peak at 392 nm and a

Table 1 Chemical Greenland Canada Xinjiang #1 Xinjiang #2 Greenlanda Theoretical compositions (wt%) of natural sodalites examined by EPMA SiO2 38.30 37.39 38.92 38.18 36.51 37.20

Al2O3 31.80 31.32 31.57 31.79 33.69 31.57

Fe2O3 0.02 0.10 0.05 0.01 0.05 MnO 0.01 0.02 0.02 0.01 MgO 0 0 0 0 0.05 CaO 0.01 0.01 0.03 0.01 0 PbO 0.03 0.01 0.02 0.03 ZnO 0.02 0.02 0.04 0.02

Na2O 25.07 24.77 24.16 25.64 24.63 19.18

K2O 0.03 0.02 0.07 0 0.02

SO3 0.59 0.07 0.08 0.11 0.12 Na 4.74 Cl 6.83 7.19 6.75 7.21 7.33 7.32 Theoretical compositions Br 0.13 0.06 0.11 0.06 calculated from the formula Ce2O3 0.04 0.06 0.06 0.08 3(Na2OAl2O32SiO2)2NaCl are shown on the right. Eu2O3 0.04 0.01 0.01 0.05 a Corresponding compositions P2O5 0.01 0.01 0 0.01 of sodalite from South Total 102.93 101.06 101.89 103.21 102.40 100.01 Greenland (Markl et al. 2001) 123 480 Phys Chem Minerals (2007) 34:477–484

Fig. 1 PL spectra of natural sodalites from 1 Greenland, 2 Xiinjiang Fig. 3 PL spectra of 1 sulfur-doped sodalite (30 wt% sulfur, 1,000C, (#2), 3 Canada, and 4 Xiinjiang (#1) at 300 K under 390 nm 30 min), 2 heat-treated sodalite (1,000C, 30 min), and 3 natural excitation sodalite (Xinjiang #2) at 300 K under 390 nm excitation

Fig. 2 Optical excitation spectra (Ex) and PL spectra (Em) of natural sodalite from Greenland at a 300 K, and b 10 K. Ex were obtained by Fig. 4 PL spectra of sulfur-doped sodalite (Xinjiang #2) (30 wt% monitoring the orange-yellow fluorescence at 626 nm, and Em were sulfur, 1,000C, 30 min) under 390 nm excitation at a 300 K, and b obtained under 390 nm excitation 10 K. The two narrow spikes at about 578 nm in (b) are Hg 576.595 and 579.065 nm lines introduced as wavelength markers full width at half maximum (FWHM) of 67 nm. In Fig. 2b, the emission spectrum at 10 K consists of a band (Em) with a clearly resolved structure and a series of maxima spaced To increase sulfur concentration, we tried to dope sulfur about 560 cm–1 (20–25 nm) apart. Each narrow band into the natural sodalites by heating the mixture of powder shows a fine structure. The excitation spectrum of the or- sodalite and sulfur (10–50 wt%) at 800–1,100C for ange-yellow fluorescence consists of a main band (Ex) with 30 min in air. Under the optimum conditions of 30 wt% a peak at 392 nm and an FWHM of 63 nm, and four small sulfur and 1,000C, the luminescence efficiencies of the bands at 257, 266, 306, and less than 200 nm, as shown in sulfur-doped sodalites from Greenland and Xinjiang (#2) Fig. 2b. The main excitation band (Ex) shows no structure were 2.4 and 7.1 times, respectively, as high as those of the even at 10 K. untreated sodalites. The luminescence efficiency of the 123 Phys Chem Minerals (2007) 34:477–484 481

Table 2 Peak wavelengths k (nm), peak wave numbers k–1 (kcm–1) and intervals (cm–1) of maxima of PL spectrum in Fig. 4b

– – S2 center in sodalite (this work) O2 center in synthetic sodalite k (nm) k–1 Interval k (nm) k–1 Interval (kcm–1) (cm–1) (kcm–1) (cm–1)

546.0 18.315 450.0 22.222 569 968 563.5 17.746 470.5 21.254 567 1032 582.1 17.179 494.5 20.222 568 1009 602.0 16.611 520.5 19.213 573 981 623.5 16.038 548.5 18.232 556 961 Fig. 5 Extended part of PL spectrum of sulfur-doped sodalite 645.9 15.482 579.0 17.271 (Xinjiang #2) (sulfur 30 wt%, 1,000C, 30 min) at 10 K under 550 918 390 nm excitation. The I peak is due to the stretching vibration of the isotopic species of 32S34S–, the S peak is due to that of the isotopic 669.7 14.932 611.5 16.353 32 – species of S2 , and the P1,P2, A, B and C peaks are due to phonon 548 958 sidebands of the S peak, as described by Kirk et al. (1965) 695.2 14.384 649.5 15.395 541 902 Figure 3 shows the PL spectra of the sulfur-doped 722.4 13.843 690.0 14.493 sodalite (30 wt% sulfur, 1,000C), heat-treated sodalite 563 920 (1,000C) and untreated sodalite (Xinjiang #2) at 300 K 753.0 13.280 736.5 13.578 under 390 nm excitation; the relative luminescence effi- 549 ciencies of the orange-yellow fluorescence of the three 785.5 12.731 samples are 100, 95 and 14, respectively. The features of – Corresponding data for the O2 center in synthetic sodalite (van the spectra are almost the same. Note that the luminescence Doorn and Schipper 1971) are shown on the right efficiency of the heat-treated sodalite without sulfur is only 5% lower than that of the sulfur-doped sodalite. Brightness sulfur-doped sodalite from Xinjiang (#2) exceeded that of of the orange-yellow fluorescence from the heat-treated the sulfur-doped sodalite from Greenland. The heat treat- sodalite under 365 nm excitation is comparable to that of ment without sulfur in air also enhanced the luminescence the yellow fluorescence from the well-known phosphor efficiencies of sodalites from Greenland and Xinjiang (#2). ZnS:Mn under 365 nm excitation.

Table 3 Peak wavelengths k (nm) and peak wave numbers k–1 (kcm–1) of fine structures on two narrow bands of the PL spectrum in Fig. 5

ISP1 P2 ABC

– S2 center in sodalite k (nm) 621.2 623.5 625.7 628.4 633.0 634.2 636.3 k–1 (kcm–1) 16.098 (60) 16.038 15.982 (56) 15.913 (125) 15.798 (240) 15.768 (270) 15.716 (322) k (nm) 643.3 645.9 648.4 651.3 655.9 657.2 659.2 k–1 (kcm–1) 15.545 (63) 15.482 15.423 (59) 15.354 (128) 15.246 (236) 15.216 (266) 15.170 (312) – S2 center in KCl k (nm) 557.5 559.4 561.3 563.3 565.5 k–1 (kcm–1) 17.937 (61) 17.876 17.815 (61) 17.752 (124) 17.684 (192) – S2 center in KBr k (nm) 568.6 569.8 571.3 572.7 575.3 577.5 k–1 (kcm–1) 17.587 (37) 17.550 17.503 (47) 17.461 (89) 17.382 (168) 17.315 (235)

–1 – Values (cm ) in parentheses show the separations from the nearest S peak. The lower part shows corresponding data for the S2 center in KCl and KBr (Kirk et al. 1965)

123 482 Phys Chem Minerals (2007) 34:477–484

Figure 4a, b shows the PL spectra of the sulfur-doped measuring system and (2) the correction of the measured sodalite (Xinjiang #2) at 300 and 10 K, respectively, under excitation spectra for the optical excitation energy. 390 nm excitation. The PL spectrum in Fig. 4a is the same As shown in Fig. 2a, b, we obtained the peak wave- as curve 1 in Fig. 3. In Fig. 4b, the two narrow spikes at lengths of the orange-yellow band (648 nm at 300 K and about 577–579 nm are markers for wavelength calibration. 645.9 nm at 10 K) and excitation band of the orange- The 576.595 and 579.065 nm lines from a low-pressure yellow fluorescence (392 nm at both 300 and 10 K). We mercury lamp were introduced into the sample surface. The presume that this study gives reliable curves of emission – FWHM of the spikes corresponds to the observation and excitation spectra of the S2 center in sodalite at 300 bandwidth of 0.35 nm. As temperature decreases, the and 10 K, because we carefully corrected the measured structure of the spectrum becomes distinct. The peak spectra as described in the above section. The excitation positions and intervals of the narrow bands of the PL spectrum consists of a main band (Ex) at 392 nm and four spectrum in Fig. 4b are listed in Table 2 (left). small bands at 257, 266, 306, and less than 200 nm, as can Figure 5 shows the extended part of the PL spectrum of be seen in Fig. 2b. This means that the obtained emission – the sulfur-doped sodalite (Xinjiang #2) at 10 K, measured spectra reflect the fluorescence only from the S2 center. If at a narrow bandwidth of 0.15 nm under 390 nm excita- the orange-yellow band includes fluorescence due to other tion. The high luminescence efficiency of the sulfur-doped center, we should have another large excitation band in sodalite enabled us to measure the emission spectra at such Fig. 2b. The origin of the small excitation band at a a narrow bandwidth. The peak positions of the fine struc- wavelength of less than 200 nm may be ascribed to the tures on two narrow bands of the PL spectrum in Fig. 5 are fundamental absorption of sodalite. The other three small shown in Table 3. excitation bands at 257, 266 and 306 nm may be ascribed to minor impurities in the sample, the origin of which is unknown. The main excitation band is attributed to the 2 2 – Discussion g fi u transition within S2 , and the orange-yellow emission band to the inverse transition. Schlaich et al. The relative luminescence efficiencies of the orange-yel- (2000) observed the blue emission band with a pronouncedP 3 – low fluorescence of the natural sodalites from Greenland, vibronicP structure, which is attributed to the u fi 3 – – Xinjiang (#2), Canada and Xinjiang (#1) are 100, 37, 8 and g transition within Se2 in synthetic sodalite. Any of 6 (Fig. 1), whereas the compositions of SO3 in these four the smallP excitationP bands in our case cannot be attributed 3 – 3 – natural sodalites are 0.59, 0.11, 0.07 and 0.08 wt%, to the g fi u transition, because no characteristic respectively, (Table 1). This supports the notion that the emission band with the vibronic structure was observed – orange-yellow fluorescence in sodalite is ascribed to S2 under 257, 266 or 306 nm excitation. ions, although the relative luminescence efficiency is not As shown in Fig. 3, the luminescence efficiency of the proportional to the composition of SO3. The composition orange-yellow fluorescence of the natural sodalite con- of SO3 (0.07 wt%) in sodalite from Canada is slightly taining sulfur is markedly enhanced by heat treatment smaller than that (0.08 wt%) in sodalite from Xinjiang (#1), without sulfur in air. Two hypotheses for this effect are but the difference between them is insignificant. suggested: One hypothesis is that thermal quenching – As mentioned above, the emission and excitation spectra changes sulfur clusters to S2 centers in sodalite. In alkali of the orange-yellow fluorescence of natural and synthetic halides activated with copper or lead, activators are quite sodalites have been reported by many investigators. The mobile in the crystal at room temperature, and aggregate to peak wavelengths of the orange-yellow band, however, form Cu or Pb clusters, as described by Tsuboi (1980), do not agree: 658 nm at 293 K and beyond 700 nm at 77 K Burslein et al. (1951), Dryden and Harvey (1969), and by Kirk (1954), 629 nm at room temperature by Hodgson Collins and Crawford Jr (1972). In particular, Pb clusters et al. (1967), about 670 nm at 110 K by Taylor et al. are formed in a few hours after thermal quenching. (1970), 677 nm at 300 K and about 680 nm at 78 K by Researchers of isolated Cu+ and Pb2+ centers in alkali Chang and Onton (1973), and 708 nm by Trashchan halides, therefore, heated the samples to 400–700C for (1978). The peak wavelengths of the excitation band of the 10–60 min, and then rapidly quenched them to room orange-yellow fluorescence have been reported: 400 nm temperature by placing them onto a copper plate at room at 77 K by Kirk (1954), and about 394 nm at 110 K temperature immediately before optical measurements by Taylor et al. (1970). The main reason for these dis- (Lopez et al. 1980). This heat treatment called ‘‘quench- crepancies is probably the unsuitable correction of the ing’’ is effective in resolving Cu and Pb clusters into iso- measured spectra. To obtain reliable spectra, one should lated Cu+ and Pb2+ centers, respectively, in alkali halides. make the suitable corrections: (1) the correction of the McLaughlan and Marshall (1970) suggested the presence – measured emission spectra for the spectral sensitivity of the of S3 radicals in synthetic sulfur-doped sodalite (blue 123 Phys Chem Minerals (2007) 34:477–484 483 ultramarine) on the basis of the measurement of the para- As shown in Table 2 (left), a series of maxima of the – magnetic resonance spectrum. From these results, the narrow bands in the orange-yellow band due to S2 center quenching treatment in this study may change sulfur in sodalite are spaced about 560 cm–1 (20–25 nm) apart. – clusters to S2 centers in sodalite. van Doorn and Schipper (1971) observed PL spectra of – 2+ 3+ Another hypothesis is that the heat treatment of soda- O2 ,Mn and Fe in synthetic sodalite at 77 K. The green 2– – – lite in air oxidizes S2 to S2 . Hodgson et al. (1967) emission band due to the O2 center shows a clearly synthesized sulfur-doped sodalite and heated it in hydro- resolved structure. The peak positions and intervals of – gen atmosphere. The sodalite obtained showed photo- maxima of the narrow bands in the O2 band in sodalite are chromism, that is, upon irradiation with UV light, the also shown in Table 2 (right). The intervals of maxima –1 – sample was colored to deep magenta, and the color was (about 560 cm ) in the S2 center are smaller than those –1 – bleached out by visible light. They observed the para- (about 980 cm ) in the O2 center, because the funda- 2– magnetic resonance spectrum of the S2 center in pho- mental vibrational frequency in the diatomic molecules tochromic sodalite and proposed a model of reversible depends on the mass of the composed atoms photochromism in which (1) an electron is transferred [m(32S) > m(16O), see Eq. (1)]. 2– under the action of UV light from S2 to a chlorine Steudel (1975) found that the linear relationships be- vacancy, (2) the electron trapped at the chlorine vacancy tween S–S bond distances dSS and S–S stretching fre- is responsible for the color, and (3) bleaching by visible quencies xSS are expressed by the following empirical light releases the electron from the chlorine vacancy equation: 2– reforming S2 (Hodgson et al. 1967). The above ÀÁ 4 1 conclusion suggests that our sodalite also includes the dssðA˚ Þ¼2:57 9:47 10 xss cm ð2Þ 2– S2 center, and that the heat treatment of sodalite in 2– – ˚ air oxidizes S2 to S2 and enhances the luminescence and Steudel (1975) determined dSS = 2.00 A for –1 – efficiency of the orange-yellow fluorescence. xSS = 600 cm of S2 . When we apply Eq. (2) to our case, –1 – In our samples, however, the luminescence efficiency xSS = 560 cm gives dSS = 2.04 A˚ for the S2 center of of the heat-treated sodalite is stable for 4 months after the sodalite in ground state. – thermal quenching. This means that the first hypothesis Fine structures on narrow bands in the PL spectra of O2 – may be invalid for sodalite. The luminescence efficiency and S2 centers in alkali halides, NaF, NaCl, NaBr, KCl, of the heat-treated sodalite from Xinjiang (#2) is com- KI, KBr, and RbBr, have been reported by Rolfe et al. parable to that of the heat-treated sodalite from Green- (1961), Rolfe (1964), Kirk et al. (1965), Rolfe (1968), and land, and the component of SO3 (0.11 wt%) in the Ikezawa and Rolfe (1973). Kirk et al. (1965) observed untreated sodalite from Xinjiang (#2) is much smaller eight peaks, labeled S, P1,P2,A,B,I,a and b, in fine – than that (0.59 wt%) of the untreated sodalite from structures on yellow emission bands in KCl: S2 and KBr: – Greenland. This discrepancy means that the above two S2 at 4 K. The peak positions of fine structures on rep- hypotheses may be invalid for sodalite. Nevertheless, it is resentative narrow bands are shown in Table 3. Kirk et al. very interesting that the luminescence efficiency of nat- (1965) ascribed the sharp S peak to the isotopic species of 32 – 32 32 – ural sodalite containing sulfur is extremely enhanced by S2 =( S– S) , the P1,P2, A and B peaks to phonon heat treatment in air (Fig. 3). Further experimental study sidebands and the I peak to the isotopic species of 32 34 – 32 34 – 32 – 32 34 – of heat-treated sodalite is required. S S =( S– S) . The details of the S2 , S S , 82 – 80 82 – 78 32 – 80 34 – As mentioned above, the structure on the orange-yellow Se2 , Se Se , Se S and Se S centers in KI band of sodalite is banded due to symmetric vibration of crystals at 4.2 K were reported by Rolfe (1968). – sulfur atoms in S2 centers (Tarashchan 1978; Marfunin In this work, the well-corresponding peaks I, S, P1,P2, 1979; Gorobets and Rogojine 2002). If we apply the di- A, B and C are observed as fine structures on narrow bands – – atomic molecule model to S2 and O2 centers in sodalite, in the orange-yellow band of sodalite at 10 K (Fig. 5; the fundamental vibrational frequency x (cm–1) is deter- Table 3). The intensity of the I peak is much smaller than mined by the following equation: that of the S peak, since the abundances of the isotopic sffiffiffiffiffi sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi species 32S–34S and 32S–32S are 8.0 and 90.3%, respec- 1 k 1 1 1 tively. If we approximate that the force constant k(32S–34S) x ¼ ¼ k þ ð1Þ 32 32 2p c l 2p c m1 m2 in Eq. (1) is equal to k( S– S), the interval between neighboring I peaks of the (32S–34S)– center in sodalite where c is the speed of light, k is the force constant, l is the should be slightly smaller (about –8 cm–1) than that 32 32 – reduced mass of the diatomic molecule, equal to (m1 m2)/ between neighboring S peaks of the ( S– S) center, 34 32 (m1 + m2), and m1 and m2 are the masses of the individual because the mass m1( S) is larger than the mass m2( S). atoms. In this case, the former (553 ± 2 cm–1) is determined as 123 484 Phys Chem Minerals (2007) 34:477–484 smaller than the latter (556 ± 2 cm–1) from Table 3. The Dryden JS, Harvey GG (1969) Dielectric and optical properties of reliability of the small difference between these values, lead-activated sodium and potassium chloride crystals. J Phys: Solid State Phys 2:603–618 however, is poor, as the accuracy of the observed wave- Gaft M, Reisfld R, Panczer G (2005) Modern luminescence –1 length is ±0.1 nm (±2 cm ). The separations of the P1,P2, spectroscopy of minerals and materials. Springer, Berlin, pp A, B and C peaks from the nearest S peak, namely, 56–59, 110–111 125–128, 236–240, 266–270 and 312–322 cm–1, respec- Gorobets BS, Rogojine AA (2002) Luminescence spectra of minerals. Reference-Book. (translated from Russian by Gorobets B and tively, indicate phonon energies with localized modes Girnis A) RPC VIMS, Moscow, p 262 – around the S2 center in sodalite. Hodgson WG, Brinen JS, Williams EF (1967) Electron spin resonance investigation of photochromic sodalites. J Chem Phys 47:3719–3723 – – – Ikezawa M, Rolfe J (1973) Zero-phonon transitions in O2 ,S2 ,Se2 , Concluding remarks and SeS– molecules dissolved in alkali halide crystals. J Chem Phys 58:2024–2038 – Reliable curves of the PL and excitation spectra of the S2 Kirk RD (1954) Role of sulfur in the luminescence and coloration of center in sodalite at 300 and 10 K were presented. It was some aluminosilicates. J Electrochem Soc 101:461–465 Kirk RD (1955) The luminescence and tenebrescence of natural and found that the luminescence efficiency of the orange-yel- synthetic sodalite. Amer Mineral 40:22–31 low fluorescence is markedly enhanced by heat treatment Kirk RD, Schulman JH, Rosenstock HB (1965) Structure in the – in air. The high luminescence efficiency of heat-treated luminescence emission of the S2 ion. Solid State Comm 3:235– sodalite enabled us to observe the luminescence spectrum 239 Lopez EJ, Jaque F, Agullo-Lopez F, Aguilar M (1980) Recombina- in detail. Fine structures on the narrow bands in the orange- tion luminescence process in NaCl. Solid State Comm 36:1001– yellow band of sodalite at 10 K were shown for the first 1005 time. Marfunin AS (1979) Spectroscopy, luminescence and radiation centers in minerals. (translated from Russian by Schiffer VV) Acknowledgments We thank Mr. Abudu Keyum, the director of Springer, Berlin, pp 216–217, 279–283 the Xinjiang Geology and Mineral Museum, for supplying the natural Markl G, Marks M, Schwinn G, Sommer H (2001) Phase equilibrium sodalites (Xinjiang #1 and #2) used in this study. The chemical constraints on intensive crystallization parameters of the Ili- compositions of the natural sodalites were determined by electron maussaq complex, South Greenland. J Petro 42:2231–2258 probe microanalysis (EPMA) at the Research Instruments Center, McLaughlan SD, Marshall DJ (1970) Paramagnetic resonance of Okayama University of Science. This study was funded by the Sci- sulfur radicals in synthetic sodalites. J Phys Chem 74:1359– entific Research Program of the Higher Education Institution of 1363 Xinjiang, China (Grant No. XJEDU2006149) and was supported by Rebane KK, Rebane LA (1974) Small molecular ions as impurity centres in crystals. Pure Appl Chem 37:161–181 the Scientific Research Foundation of Xinjiang Normal University, – China. Rolfe J (1964) Low temperature mission spectra of O2 in alkali halides. J Chem Phys 40:1664–1670 – – – Rolfe J (1968) Emission spectra of S2 ,Se2 , and SeS ions in KI crystals. J Chem Phys 49:4193–4197 References Rolfe J, Lipsett FR, King WJ (1961) Optical absorption and fluorescence of oxygen in alkali halide crystals. Phys Rev Aierken Sidike, Kusachi I, Yamashita N (2006a) Yellow fluorescence 123:447–454 from baghdadite and synthetic Ca3(Zr,Ti)Si2O9. 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J Electron Mater 2:17–46 Taylor MJ, Marshall DJ, Forrester PA, McLaughlan SD (1970) Collins WC, Crawford JH Jr (1972) Polarization of luminescence in Colour centres in sodalites and their use in storage displays. NaCl:Pb2+ and KCl:Pb2+. Phys Rev B 5:633–641 Radio Electro Eng 40:17–25 + Denks VP, Dudel’zak AE, Lushchik ChB, Ruus TV, Soshchin NP, Tsuboi T (1980) Absorption spectra of heavily Cu -doped KCl, SrCl2 Trofimova TI (1976) Recombination luminescence and color and KI crystals. J Chem Phys 72:5343–5347 – 2+ 3+ centers of cathodochromic sodalites (in English) J Appl Spect van Doorn CZ, Schipper (1971) Luminescence of O2 ,Mn and Fe 24:23–28, translated from Zh Prik Spekt (in Russian) 24:37–43 in sodalite. Phys Lett A 34:139–140

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